This invention relates to the field of railroad grade crossings where highway or street thoroughfares cross railroad tracks.
Such crossing have long been a source of difficulty for maintenance of thoroughfares because of the discontinuity in paving that they necessarily require and the associated free standing structure filling the gap between each pair of rails. Numerous structures fabricated from wood, rubber and metal have been developed and installed to meet such needs. However, virtually all such structures have suffered from difficulty and expense of installation, limited useful life and expense and difficulty of replacement. When such replacement has been required, it creates additional problems for a busy thoroughfare where it is necessary to divert or block traffic while the crossing structure is replaced or repaired.
The difficulty in developing and installing simple crossing structures relates to the conflicting requirements for the railway and the roadway of the vehicular thoroughfare crossing the railway. Attachment of the crossing structure to the rails themselves is unsatisfactory for several reasons. First, the rails which run transverse to the roadway will necessarily undergo some deflection caused by the weight of train wheels passing along the rails. Such deflection is compensated for by the roadbed provided beneath the crossties to which the rails are attached. However, such flexing of the rails conflicts with the requirements of rigidity necessary for the thoroughfare. For this reason it is necessary that the grade crossing structure be supported by some means other than by direct contact with the rails. Additionally, connection of the grade crossing structure directly to the rails themselves would tend to transmit the heavy and frequent pounding caused by the passage of heavy trucks thereover directly to the rail, likely causing a fatiguing and possibly premature failure of the rails. This is one reason that such direct connection of the crossing structure to the rails themselves generally is not permitted.
A primary problem associated with the prior art grade crossing structures has been the difficulty of fixing the structures in place while still permitting reasonable capability for removal and replacement. The positioning has been especially difficult with respect to portions of the grade crossing structure that are immediately adjacent the rail. The problems have included the difficulty of maintaining the desired spacing of the grade crossing decking from the rail to accommodate the flanges of the train wheels, the minimizing of that gap in order to provide the smoothest surface possible for vehicular traffic and avoidance of such gap becoming filled with foreign objects, thus creating a risk of potential derailment of a train.